Myopia and glaucoma are highly prevalent ophthalmic disorders worldwide, and contribute significantly to ocular morbidity. There is substantial evidence that genetic factors play a significant role in the development of non-syndromic myopia and glaucoma. We propose to perform mapping studies for well-characterized twin populations in the United Kingdom and Australia in order to ultimately identify implicated genes for these disorders, and related ocular parameters. This will provide a fundamental molecular understanding of how these disorders develop, and may lead to directed physiologic (i.e. pharmacologic, gene therapy) interventions. Public Health Relevance Statement: The goals of this project are to gain a greater understanding of the genetic basis of the eye disorders myopia and glaucoma. Achievement of this goal requires cooperative efforts and large sample sizes. We have created an international collaboration of large complementary twin studies, from the USA, Australia, and United Kingdom. State-of-the-art molecular genetics and statistical tools will be used to correlate genetic with clinical information using linkage and association approaches. This effort may lead to effective therapies for these potentially blinding disorders.